I'd divide it a little differently. I'd do story/plot and rules/mechanics GMs separately. They'd both get to control the same NPCs, but one would speak for them and the other would handle the dice.

I've heard of some success between two GMs with laptops. They could run the game in real time but AIM messages back and forth without the players noticing. GMs need to confer with each other when decisions are improvised, but you also don't want to stop the game so the GMs can discuss things. This seems like a reasonable solution if the laptops are available.